Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

暴力解法就不列出来了，上一个比较好理解且高效的方法：

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target)
    {
        int n = nums.size();
        unordered_map<int, int> hash;
        vector<int> res;

        for (int i = 0; i < n; ++i)
        {
            int solu = target - nums[i];

            if (hash.find(solu) != hash.end())
            { 
                //Find!
                res.push_back(i);
                res.push_back(hash[solu]);
                return res;
            }

            //Not Find
            hash[nums[i]] = i;
        }
    }
};